1. Field of the Invention
The present invention relates to a clutch mechanism, especially for a motor vehicle.
2. Description of the Related Art
In general terms the invention relates to a friction clutch, especially for a motor vehicle, and more particularly relates to a clutch equipped with a take-up or compensating device for wear which is due in particular to wear in the friction liner or liners, this device working to the extent that wear takes place in the liner or liners.
The invention relates to the friction clutch mechanism which is included in such clutches.
A conventional clutch mechanism includes, in particular, a rear cover plate, at least one front pressure plate coupled in rotation to the cover plate while being displaceable axially with respect to the latter, engagement means carried by the pressure plate, and axially acting clutch engagement means which act between the cover plate and the engagement means.
The clutch also includes a reaction plate which is part of an engine flywheel, which may be in two parts so as to form a damped flywheel or a flexible flywheel, mounted in rotation on a first shaft, which is typically a driving shaft such as the crankshaft of the internal combustion engine associated with the clutch, and supporting through its outer periphery the cover plate to which the pressure plate is attached with axial mobility.
The pressure plate is fixed in rotation to the cover plate and the reaction plate, while being displaceable axially under the action of axially acting clutch engagement means controlled by declutching means.
The declutching means may consist in a known way of helical springs, or two Belleville rings mounted in series, which are acted on by declutching levers that constitute the declutching means.
Generally, the clutch engaging and declutching means are both part of a common component, for example a metallic diaphragm which bears on the base of the cover plate. The diaphragm may be mounted in series or in parallel with a Belleville ring so as to provide assistance to the declutching force.
A friction disc, which typically carries friction liners at its outer periphery and which is fixed in rotation to a shaft, typically a driven shaft such as the input shaft of the gearbox of the propulsion engine unit, is interposed between the pressure plate and the reaction plate in such a way as to be gripped between them when the clutch is in its engaged position, for transmitting the torque from the driving shaft to the driven shaft. Conventionally, the friction liners are mounted on an axially elastic support member, which is coupled rigidly or elastically to a hub that is mounted in rotation on the driven shaft. Thanks to this arrangement, the friction disc assists the diaphragm during the declutching operation of the clutch.
In another version, the support is encapsulated within a friction liner, in such a way that the friction disc has only one liner and the support is axially rigid.
Conventionally, the clutch engaging means, the cover plate and the pressure plate are part of a unitary assembly which is referred to as a friction clutch mechanism.
The clutch engaging means control the axial displacement of the pressure plate when they are actuated by a clutch release bearing through declutching means.
In the course of the working life of such a clutch, the friction liner or liners and the counter-acting materials, pressure and reaction plates, become worn, which causes a variation to occur in the axial position of the pressure plate and that of the axially acting clutch engaging means, as well as the clutch release bearing, and the result of this is a variation in the gripping force exerted between the friction disc on the one hand and the pressure and reaction plates on the other, because of the modifications of the working conditions of the clutch engaging means. The force which is necessary for disengagement is thereby affected. By giving such a clutch a wear compensating device these disadvantages are avoided, and the clutch engaging means, together with the clutch release bearing, which is typically in constant engagement on the clutch engaging means, then occupies the same position when the clutch is in its engaged condition, so that the axial size of the clutch is reduced.
In French patent application FR-A-2 753 503, applied for on Sep. 17, 1996, there is proposed a wear compensating device which comprises, firstly, ramp means carried by the pressure plate, which carry an external set of teeth and which are placed between the pressure plate and the engagement means so as to constitute a pressure plate of variable thickness between its friction face and the engagement means, and including, secondly, a cassette which is mounted in a housing of the cover plate and which includes a worm in cooperation with the set of teeth of the ramp means, and of the type in which the engagement means, the external set of teeth and the ramps are all part of a single component, in the form of an annular ring carried by the pressure plate.
The worm of the cassette is in cooperation with the teeth of the set of teeth that are part of the adjusting ramp ring which is placed between the clutch engaging means and the pressure plate.
The worm is in cooperation both with the set of teeth and with means for driving in rotation which comprise a helical spring, and which are rendered operational by wear in the friction liners when the clutch is engaged. The worm is mounted tangentially with respect to the set of teeth associated with it.
In another version, the set of teeth is part of an intermediate member, as described in the document FR 98 11991 applied for on Sep. 23, 1998. The ramp means are in all cases fixed to the set of teeth for rotation with the latter.
The arrangement of a cassette at the outer radial periphery of the mechanism, and especially of the cover plate, results in a static and dynamic imbalance of the mechanism, which gives rise to vibrations that adversely affect good operation of the clutch.
In order to overcome this disadvantage, the invention proposes a clutch mechanism which is characterised in that the cover plate carries at least one means for prebalancing or balancing in order to compensate for imbalance that is due to the cassette of the compensating device.
The prebalancing means enables the assembly consisting of the cover plate and the cassette to be balanced beforehand, and resides in the provision of a prebalancing rivet and/or a prebalancing mass. The balancing means enables the clutch mechanism to be balanced finally, and consists for example of a balancing rivet.
In accordance with further features of the invention:
the cover plate includes a plurality of housings which are spaced apart circumferentially, and in one of which the cassette is mounted, at least one other of the housings constituting a mounting zone for a prebalancing means such as a prebalancing rivet;
each housing includes a transversely oriented rear base portion;
the base portion of the housing in which the cassette is mounted includes a window;
the transverse base portion of the said further housing constitutes the mounting zone for at least one prebalancing rivet and/or a prebalancing mass;
the transverse base portion of the said further housing constitutes the mounting zone for three prebalancing rivets;
the pressure plate is coupled in rotation to the cover plate by tongues, deformable elastically in the axial direction and having at least one end fixed to the cover plate or to the pressure plate by means of a rivet that constitutes a prebalancing rivet of the mechanism;
the rivet for fastening one end of a tongue to the cover plate is a prebalancing rivet which is diametrically opposed to the cassette;
the cover plate includes an external radially oriented flange for fastening the cover plate to a reaction plate and having holes arranged for fastening at least one balancing rivet;
each balancing rivet is fixed in the region of a widened zone of the said flange which is formed in an aperture for the passage through it of the heads of members for fastening the cover plate to the reaction plate;
the said aperture is formed in an axially oriented skirt which joins the said flange to the transverse base portion of the cover plate.
In another version, the prebalancing rivets are replaced at least partly by masses. In that case, it is no longer essential to provide a prebalancing rivet associated with the tongues.